Recently, a solid light emitting element has been widespread as a light source for illumination instead of an incandescent lamp or a fluorescent lamp. The solid light emitting element is a light emitting diode, an organic electro luminescence (EL) element, or the like. For example, JP 2012-204026 A (hereinafter referred to as “document 1”) discloses, as a lighting device for turning on a light source constituted of a light emitting diode (LED), a lighting device (a solid light source lighting device) that is configured to adjust (dim) light intensity of an LED depending on a dimming signal received from a dimmer.
Incidentally, examples of a dimming processing for an LED include a dimming processing (hereinafter referred to as a “DC dimming processing”) for changing the amount of a current continuously flowing through an LED and a processing (hereinafter referred to as a “burst dimming processing”) for frequently turning on/off electric conduction to an LED to change a ratio (a duty ratio) of an electric-conduction period to a whole period. In addition, like a conventional example described in document 1, there is also a case of lighting an LED by combining the DC dimming processing and the burst dimming processing.
Incidentally, a switching power supply circuit is normally used in a lighting circuit for lighting the LED. Then, in the burst dimming processing, the electric-conduction period, during which the switching power supply circuit performs a switching operation, more decreases as a dimming level more decreases. On the other hand, even if the lengths of the electric-conduction periods are same, regarding the number of times for the switching operation, dispersion is generated among the electric-conduction periods. The switching operation is performed by the switching power supply circuit during the electric-conduction period. Therefore, the light intensity of the light source is also changed due to the dispersion. In a case where the electric-conduction period is comparatively long, that is, in a case where brightness instructed by the dimming level is comparatively high, because the changing of the light intensity caused by the dispersion of the number of times for the operation is not recognized by a user, there is hardly problem.
However, in a case where the electric-conduction period is comparatively short, that is, in a case where the brightness instructed by the dimming level is comparatively low, the changing of the light intensity caused by the dispersion of the number of times for the operation is easily recognized by a user as a flicker.